1. Field of the Invention
The present invention relates to a liquid phase growth method of a silicon crystal, a method for producing a solar cell, and a liquid phase growth apparatus and, more particularly, to a liquid phase growth method that permits continuous growth and volume production.
2. Related Background Art
Liquid phase growth methods have the advantage of the capability of obtaining crystals with high quality close to stoichiometric compositions because of crystal growth from the quasi-equilibrium state and are used in production of LEDs (light-emitting diodes), laser diodes, and so on, as techniques already established in such compound semiconductors as GaAs. Recently, attempt has been made to utilize the liquid phase growth of Si in order to obtain a thick film (for example, Japanese Patent Application Laid-Open No. 58-89874) and application to solar cells is also under research.
In the conventional liquid phase growth methods, in general, a solution containing a substance for growth as a solute is cooled into a supersaturated state to deposit the excess solute (the substance for growth) on a substrate. On that occasion, it is necessary to preliminarily dissolve the solute into a solvent until saturated, prior to depositing (or growing) the solute on the substrate. Ordinary methods for dissolving the solute into the solvent include one for preliminarily mixing the solute in an amount enough to saturate at a temperature during the dissolution into the solvent and heating the solvent, and one for heating a large amount of a base material of the solute (over a saturation amount) in contact with the solvent and keeping it at the dissolving temperature to saturate. In the former case, a newly weighed amount of the solute is charged into the solvent or the old solvent is replaced by another solvent in which the solute was preliminarily dissolved, after every completion of growth. In the latter case, the base material of the solute is taken into and out of the solvent before or after the growth and the base material will be used up at last to cause some harm in taking it into or out of the solvent or result in an insufficient dissolved amount. Therefore, the old base material needs to be replaced by a new base material. In either case, time loss occurs, because the apparatus is stopped for supplying the raw material when used up or because the growth is suspended. Therefore, the methods according to the conventional techniques had the problem in terms of volume productivity.
The present invention has been accomplished as a consequence of intensive and extensive research by the inventors in order to solve the problem in the conventional techniques as discussed above and an object of the present invention is, therefore, to provide a liquid phase growth method that is simple and easy and that has high volume productivity.
Therefore, the present invention provides a liquid phase growth method of a silicon crystal comprising a step of injecting a source gas comprising at least silicon atoms into a solvent to decompose the source gas and, simultaneously therewith, dissolving the silicon atoms into the solvent, thereby supplying the silicon atoms into the solvent, and a step of dipping or contacting a substrate into or with the solvent, thereby growing a silicon crystal on the substrate.
Further, the present invention provides a method of producing a solar cell comprising at least a step of forming a silicon layer by liquid phase growth; the method comprising a step of injecting a source gas comprising at least silicon atoms into a solvent to decompose the source gas and, simultaneously therewith, dissolving the silicon atoms into the solvent, thereby supplying the silicon atoms into the solvent, and a step of dipping or contacting a substrate into or with the solvent, thereby growing a silicon crystal on the substrate to form said silicon layer.
Moreover, the present invention provides a liquid phase growth apparatus of a silicon crystal comprising means for holding a solvent in which silicon atoms are dissolved, and means for dipping or contacting a substrate into or with the solvent, the apparatus further comprising means for injecting a source gas comprising at least silicon atoms into the solvent.
Further, the present invention provides a liquid phase growth apparatus of a silicon crystal comprising a solvent reservoir for holding a solvent in which silicon atoms are dissolved, a source gas inlet pipe having an opening portion in the solvent held in the solvent reservoir, a wafer cassette for holding a substrate, the wafer cassette being arranged to be freely taken into or out of the solvent held in the solvent reservoir, and a heater.
Moreover, the present invention provides a liquid phase growth apparatus of a silicon crystal comprising a solvent reservoir and a growth vessel each for holding a solvent in which silicon atoms are dissolved, a pipe for circulating the solvent between the solvent reservoir and the growth vessel, a source gas inlet pipe having an opening portion in the solvent held in the solvent reservoir, a wafer cassette for holding a substrate, the wafer cassette being arranged to be freely taken into or out of the solvent held in the growth vessel, and a heater.
In addition, the present invention provides a liquid phase growth apparatus of a silicon crystal comprising a solvent reservoir for holding a solvent in which silicon atoms are dissolved, a pipe both ends of which are connected to the solvent reservoir and which has an aperture portion except for the both ends, the pipe being provided for circulating the solvent, a source gas inlet pipe having an opening portion in the solvent held in the solvent reservoir, a holding member for holding a substrate so that the substrate is in contact with the solvent at the aperture portion, and a heater.